As for the author’s statement that they are fighters, and his restricting it to fighters, this requires further consideration.
The correct view is that it includes the fighters, their weapons, and everything that assists jihad in the cause of Allah. Even guides who direct them to the locations of combat have a share of zakah, for Allah says, “in the cause of Allah,” and does not say, “for the fighters.” This indicates that what is meant is everything connected with jihad, since this is part of jihad in the cause of Allah.
May weapons for fighting in the cause of Allah be purchased with zakah?
According to the author’s view, this is not permissible; rather, it is to be given to the fighter himself.
According to the correct view, however, it is permissible to purchase with it weapons with which to fight in the cause of Allah—especially since it is coordinated with a noun governed by the preposition “in,” which denotes circumstance rather than ownership. Indeed, it too is governed by “in”: “and in the cause of Allah.”
Accordingly, the preponderant view is that the words, “in the cause of Allah,” encompass the fighters and the weapons and other things they require.
As for the author’s statement, “the volunteers who are not registered on the military payroll,” the apparent meaning of his words is that those who are registered on the payroll are not to be given zakah. This is correct if their stipend is sufficient for them. But if it is not sufficient, they are to be given from zakah what will suffice them.
Indeed, if someone were to say that they may be given zakah without qualification, there would be some basis for that view. However, the rationale behind what the author says is that, when they are supported from the Muslims’ public funds for their jihad, there is no need to give them zakah, since what they receive from the public treasury renders them independent of zakah.